They show that that there were no council wards in Carmarthenshire and Ceredigion in 2011 where more than 70% of the population could speak Welsh - a key target for the Welsh government.

Overall there were fewer places where at least 70% of people speak Welsh, down from 59 in 2001 - or 7% - to 49 in 2011, which is 6%.

Apart from one ward in Conwy, all the places where 70% of people speak Welsh were in Gwynedd or on Anglesey.

'Great concern'

Cymdeithas yr Iaith Gymraeg (Welsh Language Society) said that in the Welsh government's language strategy, there was a target by 2011 to halt the decline in the number of communities where Welsh is spoken by over 70% of the population.

Chair Robin Farrar said the figures showed ministers had "failed".

The language and its communities face a crisis, and the government needs new policies to ensure that the language and its communities thrivesRobin Farrar, Cymdeithas yr Iaith Gymraeg

"These results are obviously a matter of great concern, especially the situation in Carmarthenshire and Ceredigion where no communities with over 70% Welsh speakers remain," he said.

"Communities of that type are absolutely essential for the language - the international evidence is completely clear.

"The language and its communities face a crisis, and the government needs new policies to ensure that the language and its communities thrives."

After the figures were published, Welsh Language Commissioner Meri Huws said her office would establish a special unit to recommend policies on protecting the language.

The new observatory will examine the effects of economic and housing policies on Welsh-speaking communities.

Laws to ensure bilingual services, including in some parts of the private sector, were passed by the last assembly.

The Welsh government and opposition politicians are now looking at practical measures to encourage people to speak Welsh in their everyday lives.

'Future work'

Ms Huws said: "The policy options we will put forward will be strategic and radical, and will be based upon hard evidence and an open civic discussion.

"We will look at examples from abroad and gather the opinions of experts in various specialised fields."

Plaid Cymru said the figures were a "setback for the Welsh language and to us all".

It is clear that not enough work is being undertaken to maintain Welsh as a community languageLeanne Wood, Leader, Plaid Cymru

Leader Leanne Wood said targets set by the Welsh Government had not not been taken seriously, adding: "It is clear that not enough work is being undertaken to maintain Welsh as a community language."

Conservative spokesperson Suzy Davies AM said the government's Welsh language strategy had been "called into question".

"However, I am much more interested in seeing the Welsh government get this right than getting into the type of political fight which could put people off using and learning Welsh," she added.

In parts of south east Wales, such as in Monmouthshire, there was an increase in the number of electoral divisions where more than 10% of people could speak Welsh.

But the Welsh government said it recognised the need to do more to "promote and facilitate" the use of the Welsh language.

"Our Welsh Language Strategy identifies the key areas that we need to focus on, to help ensure the language's sustainability," a spokesperson said.

"The census figures will be used to inform current and future work on the Welsh language and we look forward to working with those who have an interest in the language, to secure its future."